I've worked at a couple of the top tech companies and have been co-founder of a startup with a successful exit.

Pros:

* Low stress. I find the most stressful thing at work is trying to figure out what my boss wants. (Small) Startups are easy -- just stay alive and find product market fit.

* Power/control. Things are small, so it's easy to know a large part of the codebase/product. This allows one to quickly make changes to support the business.

Cons:

* Pay. This has been well documented in this thread.